Optimizing Stop Spacing for Speed

Stop spacing is an important part of any transit service; Jarrett Walker’s Human Transit blog has an entire series of posts with technical details of the trade-off between duplicate coverage and coverage gaps, starting with this one. The basic tension is that the closer the stops, the less transit users need to walk, but the more frequently the bus needs to stop. This is no small matter; a bus takes time to pull out of traffic, slow down and stop, open the doors, board, and then accelerate and get back into traffic.

This not only slows down the riders already on the bus, but it also costs money – driver time is the main source of operating cost, and a bus that finishes the route faster is a bus that can turn around and make another run sooner, reducing headways. Closely spaced stops provide little benefit; being served by two stops is no improvement, and the walk is usually not shortened by much.

A number of transit operators, including in Seattle, Portland and San Francisco have engaged in exercises in route optimization and stop consolidation in recent years with positive result. A 2006 study of a route optimization in Portland concluded that removing a number of closely-spaced stops on a route reduced the travel time by 29 seconds per stop removed (although conservative schedulers reduced the travel time savings to 7 seconds), with no loss of ridership.

This recent discussion on the forums of Skyscraperpage.com (including TransitCamp members) identified a number of potential candidates for stop consolidation, starting with the #2 southbound downtown, where it stops on Centre Street at James Short Park north of 5th Avenue, then stops again one block south between 5th and 6th, then turns the corner and stops on 6th Avenue before 1st St SW at Suncor Centre. Three stops in three blocks; it may be faster to walk.

A couple of other examples include the #7 in Marda Loop, which stops on every single block going down 33rd Avenue, then turns at 20th St and immediately stops again. Or the #302 in Quarry Park, stopping on Quarry Park Blvd north of the shopping centre, then just around the corner on 18th St – only 250m walking distance apart – and on a “BRT” route to boot.

For a more detailed example, let’s look at a segment of the #3, southbound in Elbow Park. As the bus goes along Elbow Drive from 26th Avenue S to Sifton Blvd, a distance of about one kilometre, there are six stops, a stop spacing of about 165 metres. A number of guidelines and studies suggest optimal spacing in the range of 300-400 metres. (European guidelines tend to be even further.) This stretch of road is a low density residential area, and the #3 is a major trunk route full of commuters by this point, so this is a particularly problematic area for too-close stop spacing.

The figure below shows the current southbound stops (white dots), and the area serviced by them within a 300m walk distance – about 4 ½ minutes walking – even shorter than Calgary Transit’s maximum walk distance of 400m.

Route 3 walk distance current

All of the areas coloured are within walking distance of these stops; the red areas are within walking distance of one stop, while the purple areas are within walking distance of two stops, and the blue are within walking distance of three (!) different bus stops. The figure below shows the coverage after a possible optimization:

Route 3 walk distance - optimized

Three of the six stops have been removed, and one of the remaining three moved slightly (from the south side of Sifton Blvd to the north side). The area shown in red is within 300m of at least one stop (there is a small bit of duplicate coverage), and the yellow areas are those that are within 300m currently, but would be outside that walking distance. They are not far outside the walk distance; mostly within 350m rather than 300m – the farthest walk distance is to the Glencoe Club; people travelling to a sports facility are probably willing to walk a little further.

This consolidation keeps almost all local residents within a five minute walk, but – based on the Portland results – will save over 20 seconds through this section alone in each direction. In 2004, Calgary Transit spent $400,000 on transit signal priority for the #3 – itself a cheap improvement relative to busways – to save about 60 seconds on average per direction over the entire route. Removing three stops takes perhaps an hour of staff time during the next schedule revision, and an hour to take the signs down.

Stop consolidation can provide substantial benefits for very little cost, and it’s well past time for Calgary Transit to look at optimizing their stop spacing.


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